Video is often processed or transformed before display. For example, additional information may be layered on top of the video, special effects may be combined with the video, and when switching from one video stream to another there may be a complex transition between the two streams.
These transformations often involve complex algorithms such as two dimensional (2D) and three dimensional (3D) geometric transformations, ray tracing, and nontrivial distortions of the images. These computations may be very time consuming, and in particular many of them may not be possible to do in real time using conventional computer hardware.